Crane jib or mast



May 5, 1970 H. E. KREX ET AL 3,509,677

CRANE JIB OR MAST Filed Aug. 16, 1968 2 Sheets-Sheet 1 Fig.

INVENT OR ATTORNEY May 5, 1970 H. E. KREX ET L 3,509,677

CRANE JIB OR MAST Filed Aug. 16, 1968 2 Sheets-Sheet 2 Fig. 4

INVENT OR BY. MA 44 flwzzg W43 ATTORNEY United States Patent O 3,509,677 CRANE JIB R MAST Helge E. Krex, Charlottenlund, and Julius N. M. Waerum,

Hellerup, Denmark, assignors to Byggeriets Maskinstationer, Aktieselskab (BMS), Copenhagen, Denmark Filed Aug. 16, 1968, Ser. No. 753,207 Int. Cl. E041) 1/32;E04c 3/38 U.S. Cl. 52-646 3 Claims ABSTRACT OF THE DISCLOSURE In a crane jib or mast comprising mutually connected lattice-girder sections the sections have dilferent sectional areas so as to be telescopable into each other and the main bars of adjacent sections are connectable by means of twoarmed levers compensating for the different sectional areas of the sections and providing an appropriate transfer of the stresses between the main bars of two adjacent sections.

BACKGROUND OF THE INVENTION This invention relates to crane jibs or masts erectable by mutually connecting a plurality of lattice-girder sections.

Such crane jibs or masts are known, e.g. for transportable cranes. All the sections of the known jibs or masts of the kind in question have identical transverse dimensions and the connecting of the sections is carried out in a simple way, viz. by means of bolts which are inserted through forks or eyes provided at the ends of the main bars of two adjacent sections. However, also a connection by means of flanges is possible.

Recently the requirements to the capacity of such cranes have increased rather rapidly as regards both lifting capacity and the heights to which the burdens are to be lifted. Thus, cranes of the kind in question having a length of the jib amounting to approximately 100 meters (110 yards) have been manufactured and it is to be expected that jibs and masts of such lengths will be common in the future. However, such lengths of the jibs and masts result in a rather serious problem, viz. how such sections should be transported.

By increasing lengths of the jib or mast the transverse dimensions of the sections will increase due to the fact that the deflection of a column increases with the square of the length of the column, and such increasing tendency to deflection may be compensated for only by increasing the transverse dimension of the sections. Therefore, a transport problem will soon arise due to the fact that in several countries an upper limit exists as regards the size of a transport trailer. E.g. in Denmark a loaded trailer should not exceed a width of 3 meters a height of 4 meters (13') and a length of 10 meters (32, 6"). A jib or mast having a length of 100 meters (110 yards) should comprise sections having the transverse dimensions: 2 x 2 square meters (16', 3" x 16', 3") so that one section only may be loaded on each trailer while on the other hand 8-10 sections will be required for each jib or mast.

In order to reduce the space requirements the sections could be manufactured with unequal transversal areas in such a manner that the sections may be telescoped into each other for transport and storage. If it were possible to do this a jib or mast of a total length of 100 meters (110 yards) would be transportable by means of two or three trailers. Moreover, a more economical form of jib or mast will be obtained, seeing that it could be made widest in the middle thereof Where the tendency to column deflection is at its maximum.

However, in putting this idea into practice great difficulties arise, viz. the question of how to transfer the con- 3,509,677 Patented May 5, 1970 siderable compression stresses created in such mast or jib by the use thereof from a smaller section to a wider section, seeing that by joining two such sections the main bars of the lattice-girder sections will not be aligned. The main bars of the smaller section will be offset inwardly with respect to the main bars of the wider section. The compression force in each main bar may easily amount to 100.000 kg. (120.000 pounds) and the offsetting between the centre line of a main bar of the smaller section from the centre line of the corresponding main bar of the wider section may easily amount to 10 cm. (4"), so that a bending moment of the order 1.000.000 kg. cm. (880.000 poundsxinches) exists at the joint between two such main bars. A bending moment of this order cannot be taken up as bending stresses in the main bars because the bending stresses, due to such a moment, will be of the same order as the compression stresses resulting from the compression forces to be expected in the jib or mast during the use thereof.

It is an object of the present invention to provide a crane jib or mast of the kind referred to above which may be easily transported and stored. It is a further object of the present invention to provide such a crane jib or mast which may be constructed in an economical way due to a varying transversal area thereof. A still further object of the present invention is to provide a crane jib or mast of the kind referred to in which the transfer of forces be tween mutually offset main bars of two adjacent sections is obtained without introducing undue bending stresses in the main bars.

SUMMARY OF THE INVENTION According to the invention, in a crane jib or mast comprising a plurality of mutually connectable lattice-girder sections, each of said sections comprising mutually parallel extending main bars mutually connected by means of lattice rods extending along the side surfaces of said sections, at least one of said sections having a sectional area smaller than the sectional area of another of said sections so as to be telescopable into said other wider section, each of the main bars of said smaller section being connectable with a main bar of said wider section by means of a disconnectable joint, each of said joints comprising a twoarmed lever, one arm of which is connectable with the end of a main bar of the wider section and the other arm of which comprises a pressure foot for abutment against said main bar at an abutment location positioned at a distance from said end thereof, said two-armed lever moreover being pivotally connected with the end of the main bar of the smaller section, the ends of the main bars of the smaller section being mutually connected by means of pressure sustaining yokes and the main bars of the wider section being mutually connected by means of connecting rods extending parallel to said side surfaces of the wider section and being connected to the main bars of the wider section at said abutment locations thereof, the angle defined by said arms of said levers being so chosen that said one arm of said levers in the connected position of said wider and smaller sections extends along a plane defined by said yokes.

By constructing the crane jib or mast as specified above, the advantage is obtained that the jib or mast may be transported within a minimum of space, viz. with sections telescoped into each other. Moreover, only moderate bending stresses will be created in the main bars of the sections in the erected position of the jib or mast due to the special design and arrangement of the two-armed levers. The main force in a main bar of the smaller section will in the transfer to a main bar of the wider section result in a inwardly directed force acting upon the end of this main bar of the wider section. Moreover, the pressure foot of the lever will result in an outwardly directed force acting upon the main bar of the wider section at a distance from the end of this main bar. However, the effects of these forces upon the end of the main bar of the wider section will result only in minor elastic deformations and therefore minor stresses. This is due to the fact that an inwardly directed movement of the ends of the main bars of the wider section is counter-acted by the pressure sustaining yokes. Moreover, due to the fact that the yokes and the arms of the levers connected to the yokes extend in the same plane, no bending moments will be created in said arms and yokes and the only effects of the forces will be a minor elastic deformation of the arms of the levers and of the pressure yokes and a corresponding small movement of the ends of the main bars of the wider sec tion. Also the pressure action exerted by the pressure foot upon the main bar of the wider section will not result in considerable elastic deformations at the pressure abutment location, seeing that the pressure abutment locations of the main bars of the wider section are mutually supported by means of the connecting rods. Moreover, due to the fact that the connecting rods extend along the side surfaces of the wider section or parallel thereto no hindrance will exist at the end of the wider section which could prevent the telescoping of the smaller section into the wider one. Therefore, after the release of the levers and after the pivoting thereof to a position inside the inner contour of the wider section the smaller section may be telescoped into the wider one.

A still further object of the present invention is to provide a crane jib or mast wherein the telescoping of a smaller section into a wider one is easily carried out and in order to achieve this object each of the levers comprise a roller arranged at a distance from the axis of said pivotal connection between said lever and said main bar of the smaller section, said distance being equal to the distance between said axis and the inner surface of the main bar of the wider section to which said one arm of said lever is connectable.

By means of this construction the advantage is obtained that the rollers may be brought into contact with the inner surfaces of the main bars of the wider section by pivoting the levers so that the telescoping is easily carried out.

In order to facilitate the pivoting of the levers referred to above said levers may be in the form of plates, and the ends of the main bars to which said levers are connected may be forked. Moreover, the pressure sustaining yokes may comprise slots at the ends thereof in alignment with the spaces between the fork arms of the main bars.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective view of two adjacent ends of two lattice-girder sections of a crane jib or mast in accordance with the invention,

FIG. 2 a detail of FIG. 1 on an enlarged scale,

FIG. 3 a side view of a detail shown in FIG. 2 wherein the two sections are joined, and

FIG. 4 the detail shown in FIG. 3 wherein the parts shown occupy positions for telescoping one of the sections into the other.

In FIGS. 1-4, 1 indicates four main bars of a latticegirder section and 2 indicates four main bars of a latticegirder section having a wider inner transversal area than the outer transversal area of the section comprising the main bars 1. The main bars 1, 2 are manufactured from tubes of square cross-section.

The main bars of each section are mutually connected by means of lattice rods extending along the side surfaces of the section. For the sake of clarity only the lattice rods 3 of the Wider section are shown in the drawing. The ends of the main bars of the smaller section are mutually connected by means of two pressure sustaining yokes 4, S which extend perpendicularly to each other in the embodiment illustrated.

Each of the main bars 1 of the smaller section is connectable with a corresponding main bar 2 of the wider section by means of a two-armed lever 6. For the sake of clarity only one lever 6 is shown in FIG. 1. However, it will be understood that an identical lever =6 is arranged at each of the corners of the structure shown.

Each lever 6 comprises, as illustrated in FIG. 2, two arms 7 and 8. Each lever 6 is fulcrurned at the lower forked end 9 (cf. FIG. 2) of the corresponding main bar 1 of the smaller section by means of a pin 10. The arm 7 is provided at the end thereof with coupling means in the form of an opening and a corresponding bolt 11 with a nut.

By means of the coupling means the arm 7 is connectable to the end of the corresponding main bar 2 of the wider section. This end is bifurcated and has openings for accommodating the bolt 11.

The end of the other arm 8 of the lever is provided with a pressure foot 12. In the joined position of the two sections the pressure foot abuts an abutment location of the main bar 2 of the wider section. The abutment location lies at a distance from the forked end of the main bar 2.

As appears from FIG. 1 connecting rods 13 are welded to the main bars 2 of the wider section at the abutment locations. In the embodiment illustrated, the connecting rods 13 exend along the side surfaces of the wider section, i.e. coplanar with the lattice rods 3 of this section.

Each of the pressure yokes 4, 5 has slots 14 at the ends and the slots 14 extend in alignment with the spaces between the fork arms of the bars 1. The levers 6 are manufactured from sheet material and after removal of the bolts 11 the levers may be pivoted from the position illustrated in FIG. 3 to the position illustrated in FIG. 4 wherein the levers are partially accommodated in the slots 14 of the pressure yokes.

Each lever 6 may, as shown in FIGS. 3 and 4, comprise a roller 15. The distance bet-ween the roller 15 and the pin 10 corresponds to the distance between the pin 10 and the inner surface of the corresponding main bar 2.

The connection between the two sections explained above makes it possible to transfer the forces of the main bars of one section to the main bars of an adjacent sectron without creating undue stresses in spite of the fact that the force of one main bar is transferred to the adjacent main bar eccentrically. This may be explained in the following way:

If it is supposed that high compression force exists in the left main rod 1 of the smaller section in FIG. 1, such force will be transferred to the lever 6 by means of the pin 10. The lever 6 will exert a downwardly directed force upon the bolt 11 equal to the force existing in the bar 1. Moreover, a bending moment will be applied to the upper end of the main bar 2 of the wider section. This is due to the fact that the arm 7 of the lever will exert an inwardly directed force-upon the end of the main bar 2 and the pressure foot 12 at the end of the other arm 8 of the lever will exert an outwardly directed force upon the main rod 2, viz. at the location at which the pressure foot abuts.

As appears from FIGS. 1 and 3, the arm 7 of the lever 6 extends in the same plane as the pressure sustaming yokes 5 in the mounted position of the sections. The inwardly directed force exerted upon the end of the main bar 2 cannot result in any considerable inwardly directed deflection of the end of the main bar 2. This is due to the fact that said deflection cannot exceed the elastic longitudinal deformation of the yoke 5 and the lever arm 7 and such deformation is negligible. On the other hand, the outwardly directed force exerted by means of the pressure foot 12 upon the main bar 2 also cannot result in any considerable deflection of the main bar 2, seeing that the outwardly directed deflection of the abutment location is counteracted by means of the connecting rods 13. Generally, the construction shown corresponds to a rigid fixing of one section into the other. Moreover, support means, e.g. support crosses within the wider section are avoided which otherwise would prevent a telescoping of the smaller section into the wider section.

If tensile stresses may be expected in the main bars 1 and 2, the main bars 2 may be provided with fasteners embracing the levers 6. Supplemented in this manner the joint shown will also be able to transfer tensile forces between the main bars. Such forces will result in inwardly directed forces at the locations of the main bars 2 referred to above as the abutment locations and such inwardly directed forces will be sustained by means of the connecting rods 13 which under such conditions will act as compression rods. An outwardly directed movement of the ends of the main bars 2 will be very moderate and correspond only to the elastic longitudinal deformations resulting from the forces existing in the yokes and the lever arms 7.

We claim:

1. Crane jib or mast, comprising a plurality of mutually connectable lattice-girder sections each of said sections comprising mutually parallel extending main bars mutually connected by means of lattice rods extending along the side surfaces of said sections, at least one of said sections having a sectional area smaller than the sectional area of another of said sections so as to be telescopable into said other wider section, each of the main bars of said smaller section being connectable with a main bar of said wider section by means of a disconnectable joint, each of said joints comprising a two-armed lever, one arm of which is connectable with the end of a main bar of the wider section and the other arm of which comprises a pressure foot for abutment against said main bar at an abutment location positioned at a distance from said end thereof, said two-armed lever moreover being pivotally connected with the end of the main bar of the smaller section, the ends of the main bars of the smaller section being mutually connected by means of pressure sustaining yokes and the main bars of the Wider section being mutually connected by means of connecting rods extending parallel to said side surfaces of the Wider section and being connected to the main bars of the wider section at said abutment locations thereof, the angle defined by said arms of said levers being so chosen that said one arm of said levers in the connected position of said wider and smaller sections extends along a plane defined by means of said yokes.

2. Crane jib or mast according to claim 1 wherein each of said levers comprising a roller arranged at a distance from the axis of said pivotal connection between said lever and said main bar of the smaller section, said distance being equal to the distance between said axis and the inner surface of the main bar of the wider section to which said one arm of said lever is connectable.

3. Crane jib or mast according to claim 1 wherein said levers have plate form and the ends of the main bars to which said levers are connectable are forked and that said pressure sustaining yokes comprising slots at the ends thereof, said slots being aligned with the fork spaces of said main bars.

References Cited UNITED STATES PATENTS HARVEY C. HORNSBY, Primary Examiner US. Cl. X.R. 2l2144 

